Wifi Extender setup - HELP!

Dear all

H E L P !

I am trying to set up a home (Mac) network using a Nighthawk Extender but can’t get it to work properly.

I 've set up the Extender with both 5GHz and 2.4GHz bands, and I can connect from my Mac to the server when I connect to [...]_5GEXT

But neither the server nor my iMac will connect to the internet.

Safari gives “not reachable” messages. Chrome tells me

  news.bbc.co.uk’s server IP address could not be found

  ERR_NAME_NOT_RESOLVED

The diagram shows what I’m trying to do. 

Can someone please walk me through what I SHOULD be doing...

I’m using the Orange DNS servers – which are reported when I log in directly to the Livebox at 192.168.1.1

TIA

Ken